This invention relates to an improved transport system for motion picture film, particularly motion picture film which is advanced intermittently when being shown by a projector.
It is a standard practice in the motion picture industry today to view film at a rate of 24 per second or 1440 frames per minute. A motion picture projector includes a transport capable of incrementally advancing the film until the next picture frame aligns with a gate while the projection light is interrupted by a shutter, of holding the film in a fixed position while the shutter is open to permit the projection light to shine through the film, then, when the shutter is again closed, to advance the film until the next frame is aligned with the gate, and to repeat this procedure. The film is advanced by an intermittently driven sprocket which engages perforations along the film edge. It is standard practice for the film to be made with four perforations per frame which are employed to incrementally pull the film through the film gate by the film sprocket. A well knwon mechanism for accomplishing the intermittent driving operation is a Geneva star wheel mechanism having a driving wheel which turns at a constant speed of 1440 rpm. Each revolution of the driving wheel rotates the star wheel 1/4 of a revolution which is sufficient to advance the film through the gate from one frame to the next succeeding frame.
For various reasons, such as economy of film and simplification of the projection apparatus, it is anticipated that more motion picture films will be made with frames having only half the height of normal frames and, therefore, two perforations per frame rather than four. Accordingly, it is desirable to have the projection apparatus capable of operating with either of these two types of film.
It is necessary at the end of the time of showing a reel of film to rewind that reel so that it will be ready for the next projection. Rewinding is accomplished by any of a number of procedures but it is most convenient to employ the same apparatus used for the projection. Rewinding at the projection speed is much too slow for many operations, principally those of commercial cinemas, and so it is important to provide a convenient rewind mechanism which will operate as quickly as possible to return the film from the take-up reel to its original position on the supply reel for feeding through a projector. Projectors which are available today do not provide all of these features.